Switching device for on-load tap changers of regulating transformers

ABSTRACT

A switching device for an onload tap changer of a regulating transformer, in which use is made, instead of contacts, of vacuum switches operable without generating an arc exteriorly, the said vacuum switches being arranged along the sides of a polygonal shape in such a manner that those vacuum switches which are operated in the same switching sequence are located in a group on one and the same side of the said polygonal shape, and operated for opening and closing actions in accordance with the switching sequence from a drive shaft through a link mechanism provided for each group, whereby maintenance of the switching device is facilitated and the operation of the vacuum switches can be controlled easily.

United States Patent Inventors Ryozi Watanabe;

Yutaka Kobayashi, both of Hitachi-shi,

Japan Appl. No. 805,487 Filed Mar. 10, 1969 Patented May 25, 1971 Assignee Hitachi, Ltd. 1 Tokyo, Japan Priority Mar. 13, 1968 Japan SWITCHING DEVICE FOR ON-LOAD TAP CHANGERS OF REGULATING TRANSFORMERS 47, 54,91; 336/90, 150; 200/11 (T.C.), 144.2,146 (A.l); 321/8 (C);307/136 Primary Examiner-J. D. Miller Assistant ExaminerGerald Goldberg Attorney-Craig, Antonelli, Stewart and Hill ABSTRACT: A switching device for an onload tap changer of a regulating transformer, in which use is made, instead of contacts, of vacuumswitches operable without generating an arc exteriorly, the said vacuum switches being arranged along the sides of a polygonal shape in such a manner that those vacuum switches which are operated in the same switching sequence are located in a group on one and the same side of the said polygonal shape, and operated for opening and closing actions in accordance with the switching sequence from a drive shaft through a link mechanism provided for each group, whereby maintenance of the switching device is facilitated and the operation of the vacuum switches can be controlled easily.

PATENTED was 19m 3581; 188

SHEET 1 [IF 6 FIG:

IN VENTURE RYOz/ war/M013 yum/ 0 many/Isl ATTORNEYS SHEET 3 [1F 6 ATTORNEYS PATENTEUHAYZSIHII I 35 11 SHEET 5 OF 6 INVENTORS Ry warm/M yurmm mamas BY W,

ATTORNEYS PATENTEDHAYZSIH?! F $5 1,1 8

I sum 5 or 6 FIG: 15

INVENTORS flyozl warm/0 5E ya 1mm many/lam BY W;

ATTORNEYS SWITCHING DEVICE FOR ON-LOAD TAP CHANGERS F REGULATING TRANSFORMERS The present invention relates to an onload tap changer for use with regulating transformers.

An onload tap changer is used for switching the voltage taps of a regulating transformer, with the load current flowing through the transformer.

The onload tap changer comprises a pair of tap selectors selectively connectable with one of the taps of the tap winding of a regulating transformer, a switching device adapted to break part of the load current and a circulating current occurring incident to shorting between adjacent taps in the course of the tap changing operation, a reversing switch for changing the polarity of the tap winding and a driving mechanism for operating the tap selectors, said switching device and said reversing switch.

The switching device normally contains in the housing thereof an insulating oil, which is contaminated by the arc occurring in each tap changing operation and must, therefore, be purified periodically.

Thus, the conventional onload tap changer of the type described above must be provided with an oil purifier and requires special care in the maintenance and inspection thereof. On the other hand, a vacuum switch having switching contacts sealed in an insulating vessel and maintained at the reduced pressure of a high degree of vacuum, has recently made a remarkable progress with improved reliability so that a switch which has a long service life, both mechanically and electrically, has now become available. As a result, a novel onload tap changer has been developed in which use is made of vacuum switches as contact means for the switching device.

However, in the case of a vacuum switch, the distance between a stationary contact and a movable contact is normally so small as to be of the order of several millimeters, therefore it is difficult in the tap changing operation to open and close the vacuum switches, corresponding to the respective contacts of the switching device, in sequence according to a switching sequence. I In addition, where a current limiting resistor is used as the current limiting element for limiting a circulating current occurring during the tap changing operationincident to shorting between adjacent taps, it is common to accelerate the speed of switching and to rate the current limiting resistor for an extremely short period, so as to reduce the size of the switching device.

Therefore, when such a current limiting'resistor is used for limiting the circulating current as described above, the individual vacuum switches must be operated at a high speed in sequence and a predetermined operational sequence of the vacuum switches can hardly be maintained. On the other hand, when the current limiting resistor and the vacuum switch are divided into a large number of subunits for the purpose of reducing the current breaking duty for each vacuum switch, the operating mechanism for each vacuum switch becomes complicated.

lt is, therefore, an object of the present invention to provide a novel and improved switching device for onload tap changers, which is so designed that the individual vacuum switches, corresponding to the respective switching contacts, can be easily opened and closed in accordance with a predetermined switching sequence.

It is another object of the present invention to provide a switching device in which the operating mechanism for each vacuum switch is simplified.

It is still another object of the invention to provide a switching device of the type specified above, in which the in- 'dividual vacuum switches can be easily opened andclosed in accordance with the predetermined operational sequence even when the switching device is used with an onload tap changer of the type comprising a large number of current limiting resistors.

in order to attain the objects set forth above, the switching device according to the present invention is so constructed that those vacuum switches which are connected directly to a pair of tap selectors which are connectable with the individual taps of a tap winding in sequence and those vacuum switches which are connected to the tap selectors through a current limiting element, are divided into groups for the respective phases of a three-phase voltage and for the operation according to the same switching sequence, and the respective groups are arranged in a single row along the sides of a polygonal shape, so that the vacuum switches in each group may be operated in sequence according to a predetermined switching sequence. According to such construction as described above, it is possible to operate the corresponding vacuum switches in all phases easily all at once.

Alternatively, where two or more vacuum switches are provided for each phase and these switches are connected with each other in parallel, the switching device of the present invention may be constructed with those vacuum switches, which are connected with each other in parallel as a group. Such a construction is advantageous in that the vacuum switches can easily be applied even to such a switching device which is operative with a large current capacity; in that the vacuum switches for each phase can be accommodated in a single insulating housing as an assembly if such is desirable, which normally it is; and in that, where the number of vacuum switches is large, the vacuum switches for the respective phases can be accommodated in independent insulating housings or the groups of vacuum switches which are operated in a predetermined switching sequence for the respective phases can be accommodated in independent insulating housings either individually or in optional combination.

Furthermore, according to the present invention the aforesaid insulating housing is constructed in the form of a cylinder, in which the individual groups of vacuum switches, which are operated in accordance with a predetermined switching sequence, are arranged, each along one side of a polygonal shape, whereby the vacuum switches can be operated from a drive shaft disposed substantially centrally of the insulating housing. In this case, the drive shaft is reciprocatively driven through a predetermined angle. This is advantageous in that the driving mechanism in a conventional rotary-type tap changer can be applied as such. Such a conventional driving mechanism for tap changers is disclosed, for example, in US. Pat. Specification No. 3,213,214.

The vacuum switches in each group may be operated from the drive shaft through a lever pivotally eccentrically mounted on the drive shaft at one end and a link having an elongate slot formed therein. Therefore, a number of levers is provided corresponding to the number of vacuum switch groups. The drive of the drive shaft is transmitted from the lever to the link and thence to each group of the vacuum switches in the order mentioned. It is, therefore, preferable that the levers and the respective links are connected in such a manner that the free ends of the respective levers, in engagement with the slots in the respective links, are displaced a predetermined distance relative to each other. For this purpose, according to the present invention the points at which the respective levers are eccentrically supported by the drive shaft are selected in a suitably varying angular relation.

Still according to the present invention, each vacuum switch or each link mechanism is provided therein with an interrupting spring for urging the vacuum switch in an opening direction. Therefore, the vacuum switch can be closed simply by applying a pressure on either the movable electrode side or the stationary electrode side, and opened upon removal of the said pressure. Such construction, as well as the abovedescribed arrangement of the vacuum switches, is effective in simplifying the transmission mechanism between the driving mechanism and the respective vacuum switches.

These and other objects, features and advantages will be apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a vertical sectional view showing an onload tap changer, comprising a switching device of this invention, disposed in the vessel of a regulating transformer;

FIG. 2 is an electric connection diagram of one phase of a one-resistor-type onload tap changer;

FIG. 3 is a diagram illustrating a switching sequence of the switching device in the one resistor-type onload tap changer;

FIG. 4 is a top plan view showing the construction of the switching device according to the present invention, which is adapted for use with the one resistor-type onload tap changer;

FIG. 5 is a vertical sectional view taken along line VV of FIG. 4;

FIG. 6 is a vertical sectional view of one form of the vacuum switch used in the present invention;

FIG. 7 is a vertical sectional view of another embodiment of the switching device according to this invention;

FIG. 8 is an electric connection diagram of one phase of a two resistor-type onload tap changer;

FIG. 9 is a top plan view schematically showing the construction of a switching device adapted for use with the two resistor-type onload tap changer;

FIG. 10 is a diagram illustrating a switching sequence of the switching device in the two resistor-type onload tap changer;

FIG. 11 is an electric connection diagram of one phase of another form of the two resistor-type onload tap changer;

FIG. 12 is a plan view schematically showing the construction of a switching device corresponding to FIG. 11;

FIG. 13 is an electric connection diagram of one phase of a four resistor-type onload tap changer;

FIG. 14 is a plan view schematically showing the construction ofa switching device corresponding to FIG. 13; and

FIG. 15 is an electric connection diagram showing the arrangement of a two resistor-type onload tap changer.

The present invention will now be described in detail with reference to the drawings.

Referring to FIG. I, there is shown an overall structure of an onload tap changer according to the present invention, which comprises a vessel 1 and a top plate 2 constituting a lid of the vessel. An insulating housing 3 is connected to the top plate 2 and is suspended in the vessel 1. Above the insulating housing 3 is provided an enclosure 4 which is secured to the top plate 2 and in which a driving mechanism is housed. A switching device 5 is accommodated in the insulating housing 3. The switching device 5 has terminals 6 provided on the sidewall and a terminal 7 provided on the bottom wall thereof, which terminals are respectively opposed by terminals 8 and 9 provided on the insulating housing 3. Thus, the switching device is electrically connected, for instance, to tap selectors through the tenninal 8 and to another terminal, constituting a neutral point, through the terminal 9. The driving mechanism, housed in the enclosure 4 and generally indicated by numeral 10, is driven from an electric motor, disposed outside of the vessel 1, through a shaft 12, bevel gears 13 and a shaft 14. The switching device 5 is operatively connected to the driving mechanism 10 by an insulating shaft 15 which is driven by the said driving mechanism in such a manner that the shaft is reciprocatively rotated through a predetermined angle. Mounted on the bottom face of the insulating housing 3 is an intermittent motion mechanism 16 which is operated from the driving mechanism 10 through a shaft 17, bevel gears 18 and 19, an insulating shaft 20, couplings 21 and 22 having a play of an angle of l80 and a shaft 23. A tap selector 24 and a reversing switch or transfer switch 25 are arranged side-byside and connected to the underside of the intermittent motion mechanism 16 to be operated thereby to perform required changing operations respectively.

Referring now to FIG. 2, there is shown, for the sake of simplicity, a circuit diagram of only one phase of a one resistortype onload tap changer to be used in a three-phase electrical circuit. A tap winding TW is provided with a plurality of oddnumbered taps 1,, t, and a plurality of even-numbered taps 1,, t, The odd-numbered taps 1,, 1, are selectively connected by a tap selector TS, in sequence, while the evennumbered taps 1,, z, are selectively connected by a tap selector TS in sequence. A first vacuum switch VS has one end connected to the tap selector TS, and the other end, for example, connected to a common terminal 0 which constitutes a neutral point. A second vacuum switch VS, has one end connected to the tap selector TS, through a current limiting resistor R and the other end to the aforesaid terminal 0. A third vacuum switch VS, has one end connected to the tap selector TS, and the other end to the terminal 0.

In the circuit described above, if the first vacuum switch VS, only is closed and the second and third vacuum switches VS and V5,, are open, a load current flows from the tap I, through the vacuum switch VS, to the terminal 0. Under such condition, therefore, the tap changer is operated at the tap i When the tap is desired to be changed from the tap T to the next adjacent tap 1 this can be attained only by closing the second vacuum switch VS, with a time delay T,, opening the first vacuum switch VS, with a time delay T closing the third vacuum switch V8,, with a time delay T and opening the second vacuum switch VS, with a time delay T Conversely, when the tap is desired to be changed from the tap to the tap t the vacuum switches are operated in a reverse way.

FIG. 3 is a switching sequence diagram representing the above-described operation of the respective vacuum switches. In the diagram, the hatched sections indicate the periods in which the respective vacuum switches are closed. In the process of the switching operation illustrated, there is a period wherein the second vacuum switch VS, and the third vacuum switch VS are closed simultaneously. A circulating current occurring in this case, incident to shorting between the adjacent taps, is limited by the current limiting resistor R. The heat capacity of the current limiting resistor R is determined by the length of the overlapping period T,. It will, therefore, be seen that the switching speed must be made high in order to minimize the overlapping period T,. On the other hand, there is a tendency that the opening and closing operation of the respective vacuum switches in accordance with a desired switching sequence becomes difficult as the switching speed increases. This is because, if the switching speed becomes high, the overlapping period T or T 4 is possibly eliminated, so that the load current is broken by the switching device or the time interval T becomes extremely short, with the possibility of both the first vacuum switch VS, and the third vacuum switch VS, being closed simultaneously causing shorting of adjacent taps.

FIGS. 4 and 5 show, by way of example, the construction of the one resistor-type switching device of the arrangement shown in FIG. 2 according to the present invention. Namely, the switching device 5 is disposed in an insulating housing 26 in the form of a cylinder. The insulating housing 26 is provided with an upper end bracket 27 and a lower end bracket 28. In the interior of the insulating housing 26 are provided the first, second and third vacuum switches for each phase of a threephase voltage. These vacuum switches are segregated into three groups, Le. a group consisting of the first vacuum switches VS,,, VS and VS,,, for the respective phases, a group consisting of the second vacuum switches VS,,, V5,, and V5,, for the respective phases and a group consisting of the third vacuum switches VS;,,, VS,,, and VS,,,, for the respective phases. These groups of vacuum switches are arranged within the insulating housing in a single row, each along one side of a regular triangular shape. The stationary electrode sides of the respective vacuum switches are supported by insulating blocks 29 which are mounted on the lower end bracket 28, each for one vacuum switch. Alternatively, these insulating blocks may be provided each for one group of vacuum switches. A conductor 30 is supported on each insulating block 29, with one end thereof connected to a terminal 6 provided on the outer wall of the insulating housing 26.

The stationary electrode sides of the first and third vacuum switches for the respective phases are each connected directly to the conductor 30 while the stationary electrode side of the second vacuum switches for the respective phases are each connected to the current limiting resistor R through a conductor 31 and thence to the conductor 30. The conductor 30 serves simultaneously as a supporting member for the current limiting resistor. R.

Extending substantially centrally axially of the insulating housing 26 is a conductive rod 32. One end of the conductive rod 32 has the movable electrode sides of the respective vacuum switches connected thereto through lead wires 33, and the other end thereof extends outwardly through the lower end bracket 28 to provide a terminal 7.

Each of the vacuum switches VS in the embodiment illustrated is constructed as shown in FIG. 6 so as to normally hold the vacuum switch open. Namely, a pair of relatively movable contacts 35a and 36a, respectively carried by a stationary electrode 35b and a movable electrode 36b, are disposed in an enclosure 34 which is maintained in a highly vacuum condition. The movable electrode 36b has one end thereof extending through a metallic bellows 37 in sealing engagement therewith an held by a pressing drum 38. The pressing drum 38 is provided in opposed relation to the enclosure 34 of the vacuum switch VS and an interrupting spring 39 is provided between the pressing drum 38 and the enclosure 34, so that the pressing drum is movable toward the enclosure against the bias of the interrupting spring 39. With such construction, it will be seen that the movable electrode 36b is operated by the pressing drum while maintaining the vacuum condition in the enclosure 34. A wiping spring 40 is disposed between the pressing drum 38 and the movable electrode 36b. The pressing drum 38 is provided with a coupling member 380 at the top end thereof. The coupling member 38a is connected to a pushing lever common for all switches in one group. By constructing the vacuum switch VS as described above, the movable electrode 36b is urged upwardly through thepressing drum 38 under the biasing force of the interrupting spring 39 and thereby the stationary contact 36a is held in an open position.

A switching drive shaft 41 is rotatably supported by a bearing member 42 provided centrally of the upper end bracket 27 and is connected to the shaft 15. The upper end bracket 27 is formed with sliding grooves 43a--43c extending radially from the center thereof. These sliding grooves are formed at locations corresponding to the respective groups of vacuum switches. A lever 44, fixedly mounted on the drive shaft 41, has threearms which are connected at the outer ends thereof with one of the ends of links 45a-45c respectively by means of a pin 46. The other ends of the links 45a45c are provided with pins 47 for sliding engagement with the respective sliding grooves 43a43c. Each of the pins 47 may have a roller 48 fitted thereon, as shown, for sliding movement in the sliding groove. The links 45a-45c are connected to the respective arms of the lever 44 in such a manner that the angular position of the connection between the link and the arm of the lever with respect to a line connecting the point of engagement between the arm and the sliding groovewith the center of the drive shaft 41 successively varies in a predetermined proportion. With such arrangement, when the switching drive shaft 42 is driven, the states of engagement between the links 45a- 45c and the respective sliding grooves 43a43c are varied successively relative to each other, with the sliding strokes of the respective links varying in the range from the outer end to the middle of the sliding groove.

A bell crank 49 is pivotally connected to the bearing member 42 by means ofa pin 50. One end of the bell crank 49 is connected to the coupling member 38a of the vacuum switch VS by a pin 51, while the other end thereof is connected to one end of a slotted link 52 by a pin 53. The slotting link 52 is in turn engaged by the pin 47 of each of the links 45a-45bq, with the pin 47 extending through a slot 52a formed6 5 in the link 52. Namely, the link mechanism for controlling the opening and closing of each vacuum switch VS is composed of the lever 44, the link 45a, 45b or 45c, the sliding groove 43a, 43); or 430, the slotted link 52 and the bell crank 49.

According to the construction shown in FIGS. 4 and 5, the link 4511 has the longest sliding stroke reaching the outer end of the sliding groove 43a, and accordingly the pin 47 received in the slot 52a of the slotted link 52 is brought into engagement with the outer end extremity of the slot 52a in the link 52, causing the bell crank 49 to rotate in a counterclockwise direction through the slotted link 52. As a result, the vacuum switches VS,,, V5,, and VS, are brought into a closed position respectively. This condition corresponds to the state of FIG. 2 wherein the first vacuum switches VS, for the respective phases are closed. Namely, the regulating transformer is operated at the tap 1 For shifting the working tap from the tap t, to I the vacuum switches for the respective phases are opened and closed according to the switching sequence shown in FIG. 3.

Namely, when the drive shaft 41 is rotated in a counterclockwise direction from the position shown in FIG. 4, the outer end of the link 45b is moved toward the outer end of the sliding groove 43b to close the second vacuum switches VS,,, VS and V8,, for the respective phases. Then, with a little time delay, the outer end of the link 45a is moved from the outer end toward the inner end of the sliding groove 43a, a'llowing the first vacuum switches VS,,, V8,, and VS, for all phases to open. As the drive shaft 41 further rotates in the same direction, the outer end of the link 450 is moved toward the outer end of the sliding groove 43c, whereby the third vacuum switches VS V8 and V8 of all phases are closed. A short while later, the outer end of the link 45b is moved from the outer end toward the inner end of the sliding groove 43b, allowing the second vacuum switches VS V8,, and V8 of the respective phases to open. When such condition has been produced, the load current flows through the third vacuum switches VS V5 and V8 only of the respective phases and thus the tap change to the tap is accomplished. Under this condition, the outer end of the link 45a, corresponding to the first vacuum switches VS,,, V8,, and VS,;,, is located at the inner end extremity of the sliding groove 43c, as is the outer end of the link 45c, corresponding to the third vacuum switches VS;,,, V8 and V8 shown in FIG. 4. In the manner described, all of the first, second and third vacuum switches for the respective phases can respectively be opened or closed all at once in accordance with the given switching sequence, by only rotating the drive shaft 41.

Although in the above description each of the vacuum switches VS constituting the switching device 5 is provided therein with an interrupting spring so as to normally urge the vacuum switch in an opening direction, the interrupting spring may be provided in the link mechanism for each group of vacuum switches as shown in FIG. 7. Namely, referring to FIG. 7 in which like numerals indicate the same parts as those shown in FIG. 5, there is shown another embodiment in which one end of the bell crank 49 of the link mechanism is extended to form an extension 49a, while a spring mount 54 is provided on the inner wall surface of the insulating housing 26, and an interrupting spring 55 is disposed between the extension 49a and the spring mount 54 According to this embodiment, it is not necessary to provide the pressing drum for each vacuum switch VS and the coupling member 38a can be connected directly to one end of the movable electrode 36b so that the structure of the vacuum switch can be simplified.

The present invention has been described and illustrated hereinabove as applied to one phase of a one resistor-type onload tap changer, but it can similarly be applied to two resistor-type, four resistor-type and even six resistontype onload tap changers. Another embodiment of the present invention wherein the invention is applied to a two resistor-type onload tap changer, is illustrated in FIGS. 8 to 10 inclusive, by way of one phase only.

As shown, the tap selector T5,, corresponding to the oddnumbered taps 1,, l of the tap winding TW has the first vacuum switch VS, connected directly thereof and also has the second vacuum switch VS, connected thereto through a current limiting resistor R,, whereas the tap selector T8,, corresponding to the even-numbered taps 1,, r, has the third vacuum switch VS, directly connected thereto and also has the fourth vacuum switch VS, connected thereto through a current limiting resistor R,,. These vacuum switches VS, to VS, are operated in accordance with a switching sequence shown in FIG. 10, similar to those in the preceding embodiment. Of these vacuum switches, the first vacuum switches VS,,, VS, andVS for the respective phases; the second vacuum switches VS,,, VS and VS,,, for the respective phases; the third vacuum switches VS VS and VS for the respective phases; and the fourth vacuum switches VS,,, VS, and VS,,,, for the respective phases, are respectively segregated into groups and these groups of vacuum switches are arranged in the insulating housing 56 along the respective sides of a square shape. All of the vacuum switches in each group are connected to a common coupling member 57a, 57b, 57c or 57d so as to be operated from the drive shaft 58 through a lever 59, a link 60a, 60b, 60c or 60d and a link mechanism now shown. As in the preceding embodiment, the vacuum switches in each phase can be opened and closed in sequence by the drive of the drive shaft 58.

The present invention in which the vacuum switches are grouped for the same switching sequence and are opened and closed by the link mechanism in group, is advantageous in simplifying the construction of the switching device, compared with a conventional one in which a switching mechanism is provided for each vacuum switch.

In a regulating transformer of large capacity, the rated load current is large and accordingly the current conducting capacity and breaking capacity of a switching device used therewith are required to be large. Where a desired current conducting capacity and breaking capacity cannot be obtained by the presently used vacuum switches or the standardized vacuum switches do not suffice the requirement, it is usually practiced to use two or more vacuum switches in parallel. The present invention is applicable even in such case. FIGS. 11 and 12 illustrate another embodiment in which the invention is applied to the case described above, by way of only one phase.

Namely, referring to FIGS. 11 and 12, a pair of the first vacuum switches V8,, and VS,,, connected in parallel with each other, are connected directly to the tap selector TS, connectable with the odd-numbered taps 1,, r whereas another pair of the second vacuum switches V8 and VS,,, connected in parallel with each other, are connected to the tap selector TS, through the current limiting resistor R,. Likewise, a pair of the third vacuum switches V5,, and VS,,,, connected in parallel with each other, are connected directly to the tap selector TS connectable with the even-numbered taps t t whereas another pair of the fourth vacuum switches V8,, and VS connected in parallel with each other,

are connected to the tap selector TS, through the current limiting resistor R, The pairs of the first to the fourth vacuum switches, which are directly connected with each other, are grouped and disposed in an insulating housing 61, each arranged along one side of a square shape. The vacuum switches in each group are coupled with a common coupling member 62a, 62b, 62c or 62d which is operatively connected to a switching drive shaft 63 through a lever 64, a link 64a, 65b, 65c or 65d and a link mechanism (not shown), to be operated therefrom.

Although the embodiment has been described and illustrated with reference to a single phase structure, a three-phase structure may be obtained by juxtaposing three of'the insulating housings 61 of the type described above in a vertical or horizontal direction, or by arranging the first to the fourth vacuum switches for the respective switches in a single housing in groups. It will also be obvious that such a construction using the vacuum switches in parallel connection can be applied to an onload tap changer comprising one or four or even more current limiting resistors.

FIGS. 13 and 14 show still another embodiment of the invention, which is a four resistor-type onload tap changer constructed according to the present invention. According to this embodiment, the vacuum switch VS connected to the first tap selector TS, directly, the vacuum switches V8: and VS connected to the tap selector TS, through current limiting resistors R, and R, respectively, the vacuum switch VS connected to the second tap selector TS, directly, and the vacuum switches VS, and VS connected to the tap selector TS through current limiting resistors R and K, respectively, for the individual phases are grouped by switching sequence and are disposed in an insulating housing 61 in the groups, each arranged along each side of a regular hexagonal shape. The groups are respectively provided with common coupling members 67a67f and these coupling members are operatively connected to a drive shaft 68 through a lever 69, links 70a- 70f and a link mechanism (not shown) respectively, to be operated therefrom, as in the preceding embodiment.

FIG. 15 shows a two resistor-type onload tap changer in which the present invention is embodied and in which a group of the first vacuum switches VS,,, V8,, and V8,, for the respective phases and a group of the fourth vacuum switches VS,,,, VS and VS,,,, for the respective phases are accommodated in an insulating housing 71, while a group of the second vacuum switches VS V5 and V8 for the respective phases and a group of the third vacuum switches VS,,, VS,,, and VS,,, for the respective phases are accommodated in an insulating housing 72. As in the preceding embodiment, the first vacuum switches are directly connected to the tap selectors TS,,, TS and TS, respectively which correspond to the odd-numbered taps of the tap windings TW,, TW and TW, for the respective phases of three-phase voltage, while the second vacuum switches are connected to the tap selectors TS,,, TS and TS, through current limiting resistors R,,, R and R,,, respectively. Likewise, the third vacuum switches and the fourth vacuum switches are connected to tap selectors TS T8 and TS directly and through current limiting resistors R R and R respectively. The other ends of the respective vacuum switches are connected to a common terminal 0 constituting a neutral point. The insulating housings 71 and 72 may be juxtaposed vertically one on top of another or arranged side-by-side horizontally. in either case, the link mechanism used is constructed such that the first, second, fourth and third vacuum switches may be operated from a drive shaft 73 through the link mechanism in a group in sequence respectively. In disposing the vacuum switches in the insulating housings 71 and 72, the first and the second vacuum switches may be combined and disposed in one insulating housing and the third and the fourth vacuum switches in another insulating housing, in lieu of the combination mentioned above.

According to such arrangement as described above, the construction of the link mechanism can be simplified as compared with the arrangement wherein the vacuum switches for the respective phases of three-phase voltage are disposed in one insulating housing. Therefore, the arrangement is particularly advantageously employed in a multiresistor-type onload tap changer comprising a large number of the second and the fourth vacuum switches.

What We claim is:

l. A switching device for an onload tap changer of a regulating transformer, comprising a plurality of first vacuum switches each connected directly to one of a plurality of first tap selectors corresponding to the odd-numbered taps of the tap winding for each phase of a three-phase voltage at one terminal and to a common terminal at the other terminal, a plurality of second vacuum switches each connected to said first tap selector through a current limiting element at one terminal and to said common terminal at the other terminal, a plurality of third vacuum switches each connected directly to one of a plurality of second tap selectors corresponding to the evennumbered taps of the tap winding for said phase at one terminal and to said commo'n terminal at the other terminal, said vacuum switches being arranged along the sides of a regular polygon, with those vacuum switches which are operated at the same time in a switching sequence being located on one and the same side of said polygonal shape in a group, and means for opening and closing the vacuum switches in each group all at once in accordance with a predetermined switching sequence.

2. A switching device for an onload tap changer ofa regulating transformer, comprising a plurality of first vacuum switches each connected directly to one of a plurality of first tap selectors corresponding to the odd-numbered taps of the tap winding for each phase of a three-phase voltage at one terminal and to a common terminal at the other terminal, a plurality of second vacuum switches each connected to said first tap selector through a current limiting element at one terminal and to said common terminal at the other terminal, a plurality of third vacuum switches each connected directly to one of a plurality of second tap selectors corresponding to the evennumbered taps of the tap winding for each phase at one terminal and to a common terminal at the other terminal, a plurality of fourth vacuum switches each connected to said second tap selector through a current limiting element at one terminal and to said common terminal at the other terminal, said vacuum switches being arranged along the sides of a regular polygon with those vacuum switches which are operated at the same time in a switching sequence being located on one and the same side of said polygonal shape in a group, and means for opening and closing the vacuum switches in each group all at once in accordance with a predetermined switching sequence.

3. A switching device for an onload tap changer ofa regulating transformer as defined in claim 2, in which said first and said third vacuum switches which are connected directly to each of the first and second tap selectors for the respective phases are one in number and said second and said fourth vacuum switches which are connected to each of said first and second tap selectors through a current limiting element respectively are at least one in number, all of said vacuum switches being segregated into four groups, a first group consisting of said first vacuum switches which are connected to the first tap selector for each phase directly, a second group consisting of said second vacuum switches which are connected to said first tap selector through a current limiting element respectively, a third group consisting of said third vacuum switches which are connected to the second tap selector for each phase directly and a fourth group consisting of said fourth vacuum switches which are connected to said second tap selector through a current limiting element respectively, and said groups of vacuum switches being arranged in such a manner that one group is located on one side of the polygonal shape independently of the other groups.

4. A switching device for an onload tap changer of the regulating transformer as defined in claim 2, in which said first and said third vacuum switches which are connected directly to each of the first and second tap selectors for the respective phases are at least two in number and are connected with each other in parallel, while said second and said fourth vacuum switches which are connected to each of said first and second tap selectors through a current limiting element respectively are provided in the same number as the number of said first vacuum switches and are connected with each other in parallel.

5. A switching device for an onload tap changer of a regulating transformer, comprising a first pair of vacuum switches each connected to one of a pair of tap selectors selectively connectable with one of the taps of the related tap winding of the transformer at one terminal and to a common terminal at the other terminal, at least one second pair of vacuum switches each connected to one of said pair of tap selectors through a current limiting resistor at one terminal and to said common terminal at the other terminal, an insulating housing for accommodating said vacuum switches and said current limiting resistors, and means for opening and closing said vacuum switches in accordance with a predetermined switching sequence, said vacuum switches being disposed in said insulating housing, with those vacuum switches which are operated in the same switching sequence being located on one and the same side of a regular polygonal shape.

6. A switching device for an onload tap changer of the regulating transformer as defined in claim 5, having a plurality of said second pairs of vacuum switches connected to current limiting resistors, in which pairs of the vacuum switches and the current limiting resistors are arranged for operation in the same switching sequence and all vacuum switches are disposed in the insulating housing in two vertical steps, with those which are operated in the same switching sequence being connected with each other in parallel.

7. A switching device for an onload tap changer of the regulating transformer as defined in claim 5, having a plurality of first pairs of vacuum switches in which pairs of the vacuum switches are disposed in the insulating housing in two vertical steps, with those which are operated in the same switching sequence being connected with each other in parallel.

8. A switching device for an onload tap changer of the regulating transformer as defined in claim 5, having a plurality of said second pairs of vacuum switches connected to current limiting resistors, in which pairs of the vacuum switches and the current limiting resistors are connected in parallel for operation in the same switching sequence, respectively, and one of said vacuum switches connected with each other in parallel and one of said current limiting resistors connected with each other in parallel are disposed in one of a pair ofjuxtaposed insulating housings, while the other one of said vacuum switches and the other one of said current limiting resistors are disposed in the other one of said current limiting resistors are disposed in the other one of said insulating housings.

9. A switching device for an onload tap changer of the regulating transformer as defined in claim 5, in which three insulating housings, respectively, accommodating the vacuum switches and the current limiting resistors are vertically juxtaposed in three steps, each for each phase of a three-phase voltage.

10. A switching device for an onload tap changer of the regulating transformer as defined in claim 5, in which three insulating housings, respectively, accommodating the vacuum switches and the currency limiting resistors are arranged sideby-side horizontally, each for each phase of a three-phase voltage.

ll. A switching device for an onload tap changer of a regulating transformer, comprising a first vacuum switch connected directly to a first tap selector selectively connectable with the odd-numbered taps of the related tap winding of the transformer at one terminal and to a common terminal at the other terminal, at least one second vacuum switch connected to said first tap selector through a current limiting resistor at one terminal and to said common terminal at the other terminal, a third vacuum switch connected directly to a second tap selector selectively connectable with the even-numbered taps of said tap winding at one terminal and to said common terminal at the other terminal, at least one fourth vacuum switch connected to said second tap selector through a current limiting resistor at one terminal and to said common terminal at the other terminal, an insulating housing for accommodating said first vacuum switch and said fourth vacuum switch, and another insulating housing for accommodating said second vacuum switch and said third vacuum switch, and means for opening and closing said vacuum switches in sequence from the first vacuum switch to the fourth vacuum switch in accordance with a tap switching sequence.

12. A switching device for an onload tap changer of the regulating transformer as defined in claim 11, in which said insulating housings are juxtaposed vertically in two steps.

13. A switching device for an onload tap changer of the regulating transformer as defined in claim 11, in which said insulating housings are arranged side-by-side horizontally.

14. A switching device for an onload tap changer of the regulating transformer as defined in claim 11, in which two of said second vacuum switches, two of said current limiting resistors connected to said respective second vacuum switches, two of said fourth vacuum switches and two of said current limiting switches connected to said respective fourth vacuum switches are provided.

15. A switching device for an onload tap changer of the regulating transformer as defined in claim 11, in which three of said second vacuum switches, three of said current limiting resistors connected to said respective second vacuum switches, three of said fourth vacuum switches and three of said current limiting switches connected to said respective fourth vacuum switches are provided.

16. A switching device for an onload tap changer of the regulating transformer as defined in claim 11, in which said first vacuum switch, said second vacuum switch, said third vacuum switch and said fourth vacuum switch are disposed in an insulating housing common for all phases of three-phase voltage.

17. A switching device for an onload tap changer of a regulating transformer, comprising a first vacuum switch group consisting of three vacuum switches each connected directly to a first tap selector for each phase selectively connectable with the odd-numbered tap group of the tap winding for each phase of three-phase voltage at one terminal and to a common terminal at the other terminal, a second vacuum switch group consisting of vacuum switches in a number being a multiple of three each connected to said first tap selector through a current limiting resistor at one terminal and to said common terminal at the other terminal, a third vacuum switch group consisting of three vacuum switches each connected directly to a second tap selector for each phase selectively connectable with the even-numbered tap group of said tap winding at one terminal and to said common terminal at the other terminal, a fourth vacuum switch group consisting of vacuum switches in a number being a multiple of three each connected to said second tap selector through a current limiting resistor, an insulating housing in which said first vacuum switch group, said second vacuum switch group, said third vacuum switch group and said fourth vacuum switch group are arranged each along one side of a square shape, a drive shaft located at the center of said square within said insulating housing and supported by said insulating housing for reciprocative rotation through a predetermined angle, a plurality oflevers each having one end supported eccentrically by said drive shaft and a plurality of link mechanisms each having one end operatively connected to the other end of each of said levers through a slotted link and the other end operatively connected to each of said vacuum switch group.

18. A switching device for an onload tap changer of the regulating transformer as defined in claim 17, in which the vacuum switches in each of said vacuum switch groups are connected by a common pressing lever which is operatively connected with each of said link mechanisms.

19. A switching device for an onload tap changer of the regulating transformer as defined in claim 17, in which each of said link mechanisms is provided with means for constantly urging the vacuum switches in the associated vacuum switch group in an opening direction.

20. A switching device for an onload tap changer of the regulating transformer as defined in claim 18, in which said pressing lever is provided with a spring for constantly urging the vacuum switches in the associated vacuum switch group in an opening direction. 1

21. A switching device for an onload tap changer of the regulating transformer as defined in claim 17, in which each of the vacuum switches in each vacuum switch group is provided with means by which said vacuum switch is constantly urged in an opening direction.

22. A switching device for an onload tap changer of the regulating transformer as defined in claim 17, in which the respective ends of said levers are eccentrically supported on supporting points of said driving shaft, said supporting points being disposed that the respective angular positions of the lines connecting said supporting points with the center of said driving shaft are successively varied in a same direction by a predetermined angle with respect to the lines connecting the middle points of the corresponding sides of said square with said center. 

1. A switching device for an onload tap changer of a regulating transformer, comprising a plurality of first vacuum switches each connected directly to one of a plurality of first tap selectors corresponding to the odd-numbered taps of the tap winding for each phase of a three-phase voltage at one terminal and to a common terminal at the other terminal, a plurality of second vacuum switches each connected to said first tap selector through a current limiting element at one terminal and to said common terminal at the other terminal, a plurality of third vacuum switches each connected directly to one of a plurality of second tap selectors corresponding to the even-numbered taps of the tap winding for said phase at one terminal and to said common terminal at the other terminal, said vacuum switches being arranged along the sides of a regular polygon, with those vacuum switches which are operated at the same time in a switching sequence being located on one and the same side of said polygonal shape in a group, and means for opening and closing the vacuum switches in each group all at once in accordance with a predetermined switching sequence.
 2. A switching device for an onload tap changer of a regulating transformer, comprising a plurality of first vacuum switches each connected directly to one of a plurality of first tap selectors corresponding to the odd-numbered taps of the tap winding for each phase of a three-phase voltage at one terminal and to a common terminal at the other terminal, a plurality of second vacuum switches each connected to said first tap selector through a current limiting element at one terminal and to said common terminal at the other terminal, a plurality of third vacuum switches each connected directly to one of a plurality of second tap selectors corresponding to the even-numbered taps of the tap winding for each phase at one terminal and to a common terminal at the other terminal, a plurality of fourth vacuum switches each connected to said second tap selector through a current limiting element at one terminal and to said common terminal at the other terminal, said vacuum switches being arranged along the sides of a regular polygon with those vacuum switches which are operated at the same time in a switching sequence being located on one and the same side of said polygonal shape in a group, and means for opening and closing the vacuum switches in each group all at once in accordance with a predetermined switching sequence.
 3. A switching device for an onload tap changer of a regulating transformer as defined in claim 2, in which said first and said third vacuum switches which are connected directly to each of the first and second tap selectors for the respective phases are one in number and said second and said fourth vacuum switches which are connected to each of said first and second tap selectors through a current limiting element respectively are at least one in number, all of said vacuum switches being segregated into four groups, a first group consisting of said first vacuum switches which are connected to the first tap selector for each phase directly, a second group consisting of said second vacuum switches which are connected to said first tap selector through a current limiting element respectively, a third group consisting of said third vacuum switches which are connected to the second tap selector for each phase directly and a fourth group consisting of said fourth vacuum switches which are connected to said second tap selector through a current limiting element respectively, and said groups of vacuum switches being arranged in such a manner that one group is located on one side of the polygonal shape independently of the other groups.
 4. A switching device for an onload tap changer of the regulating transformer as defined in claim 2, in which said first and said third vacuum switChes which are connected directly to each of the first and second tap selectors for the respective phases are at least two in number and are connected with each other in parallel, while said second and said fourth vacuum switches which are connected to each of said first and second tap selectors through a current limiting element respectively are provided in the same number as the number of said first vacuum switches and are connected with each other in parallel.
 5. A switching device for an onload tap changer of a regulating transformer, comprising a first pair of vacuum switches each connected to one of a pair of tap selectors selectively connectable with one of the taps of the related tap winding of the transformer at one terminal and to a common terminal at the other terminal, at least one second pair of vacuum switches each connected to one of said pair of tap selectors through a current limiting resistor at one terminal and to said common terminal at the other terminal, an insulating housing for accommodating said vacuum switches and said current limiting resistors, and means for opening and closing said vacuum switches in accordance with a predetermined switching sequence, said vacuum switches being disposed in said insulating housing, with those vacuum switches which are operated in the same switching sequence being located on one and the same side of a regular polygonal shape.
 6. A switching device for an onload tap changer of the regulating transformer as defined in claim 5, having a plurality of said second pairs of vacuum switches connected to current limiting resistors, in which pairs of the vacuum switches and the current limiting resistors are arranged for operation in the same switching sequence and all vacuum switches are disposed in the insulating housing in two vertical steps, with those which are operated in the same switching sequence being connected with each other in parallel.
 7. A switching device for an onload tap changer of the regulating transformer as defined in claim 5, having a plurality of first pairs of vacuum switches in which pairs of the vacuum switches are disposed in the insulating housing in two vertical steps, with those which are operated in the same switching sequence being connected with each other in parallel.
 8. A switching device for an onload tap changer of the regulating transformer as defined in claim 5, having a plurality of said second pairs of vacuum switches connected to current limiting resistors, in which pairs of the vacuum switches and the current limiting resistors are connected in parallel for operation in the same switching sequence, respectively, and one of said vacuum switches connected with each other in parallel and one of said current limiting resistors connected with each other in parallel are disposed in one of a pair of juxtaposed insulating housings, while the other one of said vacuum switches and the other one of said current limiting resistors are disposed in the other one of said current limiting resistors are disposed in the other one of said insulating housings.
 9. A switching device for an onload tap changer of the regulating transformer as defined in claim 5, in which three insulating housings, respectively, accommodating the vacuum switches and the current limiting resistors are vertically juxtaposed in three steps, each for each phase of a three-phase voltage.
 10. A switching device for an onload tap changer of the regulating transformer as defined in claim 5, in which three insulating housings, respectively, accommodating the vacuum switches and the currency limiting resistors are arranged side-by-side horizontally, each for each phase of a three-phase voltage.
 11. A switching device for an onload tap changer of a regulating transformer, comprising a first vacuum switch connected directly to a first tap selector selectively connectable with the odd-numbered taps of the related tap winding of the transformer at one terminal and to a common terminal at the other terminal, at least one sEcond vacuum switch connected to said first tap selector through a current limiting resistor at one terminal and to said common terminal at the other terminal, a third vacuum switch connected directly to a second tap selector selectively connectable with the even-numbered taps of said tap winding at one terminal and to said common terminal at the other terminal, at least one fourth vacuum switch connected to said second tap selector through a current limiting resistor at one terminal and to said common terminal at the other terminal, an insulating housing for accommodating said first vacuum switch and said fourth vacuum switch, and another insulating housing for accommodating said second vacuum switch and said third vacuum switch, and means for opening and closing said vacuum switches in sequence from the first vacuum switch to the fourth vacuum switch in accordance with a tap switching sequence.
 12. A switching device for an onload tap changer of the regulating transformer as defined in claim 11, in which said insulating housings are juxtaposed vertically in two steps.
 13. A switching device for an onload tap changer of the regulating transformer as defined in claim 11, in which said insulating housings are arranged side-by-side horizontally.
 14. A switching device for an onload tap changer of the regulating transformer as defined in claim 11, in which two of said second vacuum switches, two of said current limiting resistors connected to said respective second vacuum switches, two of said fourth vacuum switches and two of said current limiting switches connected to said respective fourth vacuum switches are provided.
 15. A switching device for an onload tap changer of the regulating transformer as defined in claim 11, in which three of said second vacuum switches, three of said current limiting resistors connected to said respective second vacuum switches, three of said fourth vacuum switches and three of said current limiting switches connected to said respective fourth vacuum switches are provided.
 16. A switching device for an onload tap changer of the regulating transformer as defined in claim 11, in which said first vacuum switch, said second vacuum switch, said third vacuum switch and said fourth vacuum switch are disposed in an insulating housing common for all phases of three-phase voltage.
 17. A switching device for an onload tap changer of a regulating transformer, comprising a first vacuum switch group consisting of three vacuum switches each connected directly to a first tap selector for each phase selectively connectable with the odd-numbered tap group of the tap winding for each phase of three-phase voltage at one terminal and to a common terminal at the other terminal, a second vacuum switch group consisting of vacuum switches in a number being a multiple of three each connected to said first tap selector through a current limiting resistor at one terminal and to said common terminal at the other terminal, a third vacuum switch group consisting of three vacuum switches each connected directly to a second tap selector for each phase selectively connectable with the even-numbered tap group of said tap winding at one terminal and to said common terminal at the other terminal, a fourth vacuum switch group consisting of vacuum switches in a number being a multiple of three each connected to said second tap selector through a current limiting resistor, an insulating housing in which said first vacuum switch group, said second vacuum switch group, said third vacuum switch group and said fourth vacuum switch group are arranged each along one side of a square shape, a drive shaft located at the center of said square within said insulating housing and supported by said insulating housing for reciprocative rotation through a predetermined angle, a plurality of levers each having one end supported eccentrically by said drive shaft and a plurality of link mechanisms each having one end operatively connected to the other end of each of said levers through a slotted link and the other end operatively connected to each of said vacuum switch group.
 18. A switching device for an onload tap changer of the regulating transformer as defined in claim 17, in which the vacuum switches in each of said vacuum switch groups are connected by a common pressing lever which is operatively connected with each of said link mechanisms.
 19. A switching device for an onload tap changer of the regulating transformer as defined in claim 17, in which each of said link mechanisms is provided with means for constantly urging the vacuum switches in the associated vacuum switch group in an opening direction.
 20. A switching device for an onload tap changer of the regulating transformer as defined in claim 18, in which said pressing lever is provided with a spring for constantly urging the vacuum switches in the associated vacuum switch group in an opening direction.
 21. A switching device for an onload tap changer of the regulating transformer as defined in claim 17, in which each of the vacuum switches in each vacuum switch group is provided with means by which said vacuum switch is constantly urged in an opening direction.
 22. A switching device for an onload tap changer of the regulating transformer as defined in claim 17, in which the respective ends of said levers are eccentrically supported on supporting points of said driving shaft, said supporting points being disposed that the respective angular positions of the lines connecting said supporting points with the center of said driving shaft are successively varied in a same direction by a predetermined angle with respect to the lines connecting the middle points of the corresponding sides of said square with said center. 